Hypothalamic Supramammillary Nucleus Selectively Excites Hippocampal CA3 Interneurons to Suppress CA3 Pyramidal Neuron Activity.

A key mode of neuronal communication between distant brain regions is through excitatory synaptic transmission mediated by long-range glutamatergic projections emitted from principal neurons. The long-range glutamatergic projection normally forms numerous en passant excitatory synapses onto both principal neurons and interneurons along its path. Under physiological conditions, the monosynaptic excitatory drive onto postsynaptic principal neurons outweighs disynaptic feedforward inhibition, with the net effect of depolarizing principal neurons. In contrast with this conventional doctrine, here we report that a glutamatergic projection from the hypothalamic supramammillary nucleus (SuM) largely evades postsynaptic pyramidal neurons (PNs), but preferentially target interneurons in the hippocampal CA3 region to predominantly provide feedforward inhibition. Using viral-based retrograde and anterograde tracing and ChannelRhodopsin2 (ChR2)-assisted patch-clamp recording in mice of either sex, we show that SuM projects sparsely to CA3 and provides minimal excitation onto CA3 PNs. Surprisingly, despite its sparse innervation, the SuM input inhibits all CA3 PNs along the transverse axis. Further, we find that SuM provides strong monosynaptic excitation onto CA3 parvalbumin-expressing interneurons evenly along the transverse axis, which likely mediates the SuM-driven feedforward inhibition. Together, our results demonstrate that a novel long-range glutamatergic pathway largely evades principal neurons, but rather preferentially innervates interneurons in a distant brain region to suppress principal neuron activity. Moreover, our findings reveal a new means by which SuM regulates hippocampal activity through SuM-to-CA3 circuit, independent of the previously focused projections from SuM to CA2 or dentate gyrus.SIGNIFICANCE STATEMENT The dominant mode of neuronal communication between brain regions is the excitatory synaptic transmission mediated by long-range glutamatergic projections, which form en passant excitatory synapses onto both pyramidal neurons and interneurons along its path. Under normal conditions, the excitation onto postsynaptic neurons outweighs feedforward inhibition, with the net effect of depolarization. In contrast with this conventional doctrine, here we report that a glutamatergic input from hypothalamic supramammillary nucleus (SuM) largely evades PNs but selectively targets interneurons to almost exclusively provide disynaptic feedforward inhibition onto hippocampal CA3 PNs. Thus, our findings reveal a novel subcortical-hippocampal circuit that enables SuM to regulate hippocampal activity via SuM-CA3 circuit, independent of its projections to CA2 or dentate gyrus.

Hippocampal astrocytic neogenin regulating glutamate uptake, a critical pathway for preventing epileptic response.

Epilepsy, a common neurological disorder, is featured with recurrent seizures. Its underlying pathological mechanisms remain elusive. Here, we provide evidence for loss of neogenin (NEO1), a coreceptor for multiple ligands, including netrins and bone morphological proteins, in the development of epilepsy. NEO1 is reduced in hippocampi from patients with epilepsy based on transcriptome and proteomic analyses. Neo1 knocking out (KO) in mouse brains displays elevated epileptiform spikes and seizure susceptibility. These phenotypes were undetectable in mice, with selectively depleted NEO1 in excitatory (NeuroD6-Cre+) or inhibitory (parvalbumin+) neurons, but present in mice with specific hippocampal astrocytic Neo1 KO. Additionally, neurons in hippocampal dentate gyrus, a vulnerable region in epilepsy, in mice with astrocyte-specific Neo1 KO show reductions in inhibitory synaptic vesicles and the frequency of miniature inhibitory postsynaptic current(mIPSC), but increase of the duration of miniature excitatory postsynaptic current and tonic NMDA receptor currents, suggesting impairments in both GABAergic transmission and extracellular glutamate clearance. Further proteomic and cell biological analyses of cell-surface proteins identified GLAST, a glutamate-aspartate transporter that is marked reduced in Neo1 KO astrocytes and the hippocampus. NEO1 interacts with GLAST and promotes GLAST surface distribution in astrocytes. Expressing NEO1 or GLAST in Neo1 KO astrocytes in the hippocampus abolishes the epileptic phenotype. Taken together, these results uncover an unrecognized pathway of NEO1-GLAST in hippocampal GFAP+ astrocytes, which is critical for GLAST surface distribution and function, and GABAergic transmission, unveiling NEO1 as a valuable therapeutic target to protect the brain from epilepsy.

Lactate Metabolism, Signaling, and Function in Brain Development, Synaptic Plasticity, Angiogenesis, and Neurodegenerative Diseases.

Neural tissue requires a great metabolic demand despite negligible intrinsic energy stores. As a result, the central nervous system (CNS) depends upon a continuous influx of metabolic substrates from the blood. Disruption of this process can lead to impairment of neurological functions, loss of consciousness, and coma within minutes. Intricate neurovascular networks permit both spatially and temporally appropriate metabolic substrate delivery. Lactate is the end product of anaerobic or aerobic glycolysis, converted from pyruvate by lactate dehydrogenase-5 (LDH-5). Although abundant in the brain, it was traditionally considered a byproduct or waste of glycolysis. However, recent evidence indicates lactate may be an important energy source as well as a metabolic signaling molecule for the brain and astrocytes-the most abundant glial cell-playing a crucial role in energy delivery, storage, production, and utilization. The astrocyte-neuron lactate-shuttle hypothesis states that lactate, once released into the extracellular space by astrocytes, can be up-taken and metabolized by neurons. This review focuses on this hypothesis, highlighting lactate's emerging role in the brain, with particular emphasis on its role during development, synaptic plasticity, angiogenesis, and disease.

APP in the Neuromuscular Junction for the Development of Sarcopenia and Alzheimer's Disease.

Sarcopenia, an illness condition usually characterized by a loss of skeletal muscle mass and muscle strength or function, is often associated with neurodegenerative diseases, such as Alzheimer's disease (AD), a common type of dementia, leading to memory loss and other cognitive impairment. However, the underlying mechanisms for their associations and relationships are less well understood. The App, a Mendelian gene for early-onset AD, encodes amyloid precursor protein (APP), a transmembrane protein enriched at both the neuromuscular junction (NMJ) and synapses in the central nervous system (CNS). Here, in this review, we highlight APP and its family members' physiological functions and Swedish mutant APP (APPswe)'s pathological roles in muscles and NMJ. Understanding APP's pathophysiological functions in muscles and NMJ is likely to uncover insights not only into neuromuscular diseases but also AD. We summarize key findings from the burgeoning literature, which may open new avenues to investigate the link between muscle cells and brain cells in the development and progression of AD and sarcopenia.

Hippocampal Neurogenesis and Neural Circuit Formation in a Cuprizone-Induced Multiple Sclerosis Mouse Model.

Cognitive impairments are key features in multiple sclerosis (MS), a progressive disorder characterized by neuroinflammation-induced demyelination in the central nervous system. To understand the neural substrates that link demyelination to cognitive deficits in MS, we investigated hippocampal neurogenesis and synaptic connectivity of adult-born neurons, which play an essential role in cognitive function. The administration and withdrawal of the combination of cuprizone and rapamycin (Cup/Rap) in C57BL/6J male mice efficiently demyelinated and remyelinated the hippocampus, respectively. In the demyelinated hippocampus, neurogenesis was nearly absent in the dentate gyrus, which was due to inhibited proliferation of neural stem cells (NSCs). Specifically, radial glia-like type 1 NSCs were shifted from a proliferative state to a mitotically-quiescent state in the demyelinated hippocampus. In addition, dendritic spine densities of adult-born neurons were significantly decreased, indicating a reduction in synaptic connections between hippocampal newborn neurons and excitatory input neurons. Concomitant with hippocampal remyelination induced by withdrawal of Cup/Rap, proliferation of type 1 NSCs and dendritic spine densities of adult-born neurons reverted to normal in the hippocampus. Our study shows that proliferation of hippocampal NSCs and synaptic connectivity of adult-born neurons are inversely correlated with the level of demyelination, providing critical insight into hippocampal neurogenesis as a potential therapeutic target to treat cognitive deficits associated with MS.SIGNIFICANCE STATEMENT To identify the neural substrates that mediate cognitive dysfunctions associated with a majority of MS patients, we investigated hippocampal neurogenesis and structural development of adult-born neurons using a Cup/Rap model, which recapitulates the hippocampal demyelination that occurs in MS patients. A shift of NSCs from a proliferatively-active state to mitotically-quiescent state dramatically decreased neurogenesis in the demyelinated hippocampus. Formation of dendritic spines on newborn neurons was also impaired following demyelination. Interestingly, the altered neurogenesis and synaptic connectivity of newborn neurons were reversed to normal levels during remyelination. Thus, our study revealed reversible genesis and synaptic connectivity of adult-born neurons between the demyelinated and remyelinated hippocampus, suggesting hippocampal neurogenesis as a potential target to normalize cognitive impairments in MS patients.

Ependymal Vps35 Promotes Ependymal Cell Differentiation and Survival, Suppresses Microglial Activation, and Prevents Neonatal Hydrocephalus.

Hydrocephalus is a pathologic condition associated with various brain diseases, including Alzheimer's disease (AD). Dysfunctional ependymal cells (EpCs) are believed to contribute to the development of hydrocephalus. It is thus of interest to investigate EpCs' development and function. Here, we report that vacuolar protein sorting-associated protein 35 (VPS35) is critical for EpC differentiation, ciliogenesis, and survival, and thus preventing neonatal hydrocephalus. VPS35 is abundantly expressed in EpCs. Mice with conditional knock-out (cKO) of Vps35 in embryonic (Vps35GFAP-Cre and Vps35Emx1-Cre) or postnatal (Vps35Foxj1-CreER) EpC progenitors exhibit enlarged lateral ventricles (LVs) and hydrocephalus-like pathology. Further studies reveal marked reductions in EpCs and their cilia in both Vps35GFAP-Cre and Vps35Foxj1-CreER mutant mice. The reduced EpCs appear to be due to impairments in EpC differentiation and survival. Additionally, both Vps35GFAP-Cre and Vps35Foxj1-CreER neonatal pups exhibit increased cell proliferation and death largely in a region close to LV-EpCs. Many microglia close to the mutant LV-EpC region become activated. Depletion of the microglia by PLX3397, an antagonist of colony-stimulating factor 1 receptor (CSF1R), restores LV-EpCs and diminishes the pathology of neonatal hydrocephalus in Vps35Foxj1-CreER mice. Taken together, these observations suggest unrecognized functions of Vps35 in EpC differentiation, ciliogenesis, and survival in neonatal LV, and reveal pathologic roles of locally activated microglia in EpC homeostasis and hydrocephalus development.SIGNIFICANCE STATEMENT This study reports critical functions of vacuolar protein sorting-associated protein 35 (VPS35) not only in promoting ependymal cell (EpC) differentiation, ciliogenesis, and survival, but also in preventing local microglial activation. The dysfunctional EpCs and activated microglia are likely to induce hydrocephalus.

Expression of Low Level of VPS35-mCherry Fusion Protein Diminishes Vps35 Depletion Induced Neuron Terminal Differentiation Deficits and Neurodegenerative Pathology, and Prevents Neonatal Death.

Vps35 (vacuolar protein sorting 35) is a key component of retromer that consists of Vps35, Vps26, and Vps29 trimers, and sortin nexin dimers. Dysfunctional Vps35/retromer is believed to be a risk factor for development of various neurodegenerative diseases. Vps35Neurod6 mice, which selectively knock out Vps35 in Neurod6-Cre+ pyramidal neurons, exhibit age-dependent impairments in terminal differentiation of dendrites and axons of cortical and hippocampal neurons, neuro-degenerative pathology (i.e., increases in P62 and Tdp43 (TAR DNA-binding protein 43) proteins, cell death, and reactive gliosis), and neonatal death. The relationships among these phenotypes and the underlying mechanisms remain largely unclear. Here, we provide evidence that expression of low level of VPS35-mCherry fusion protein in Vps35Neurod6 mice could diminish the phenotypes in an age-dependent manner. Specifically, we have generated a conditional transgenic mouse line, LSL-Vps35-mCherry, which expresses VPS35-mCherry fusion protein in a Cre-dependent manner. Crossing LSL-Vps35-mCherry with Vps35Neurod6 to obtain TgVPS35-mCherry, Vps35Neurod6 mice prevent the neonatal death and diminish the dendritic morphogenesis deficit and gliosis at the neonatal, but not the adult age. Further studies revealed that the Vps35-mCherry transgene expression was low, and the level of Vps35 mRNA comprised only ~5-7% of the Vps35 mRNA of control mice. Such low level of VPS35-mCherry could restore the amount of other retromer components (Vps26a and Vps29) at the neonatal age (P14). Importantly, the neurodegenerative pathology presented in the survived adult TgVps35-mCherry; Vps35Neurod6 mice. These results demonstrate the sufficiency of low level of VPS35-mCherry fusion protein to diminish the phenotypes in Vps35Neurod6 mice at the neonatal age, verifying a key role of neuronal Vps35 in stabilizing retromer complex proteins, and supporting the view for Vps35 as a potential therapeutic target for neurodegenerative diseases.

Pten loss results in inappropriate excitatory connectivity.

Pten mutations are associated with autism spectrum disorder. Pten loss of function in neurons increases excitatory synaptic connectivity, contributing to an imbalance between excitation and inhibition. We aimed to determine whether Pten loss results in aberrant connectivity in neural circuits. We compared postnatally generated wild-type and Pten knockout granule neurons integrating into the dentate gyrus using a variety of methods to examine their connectivity. We found that postsynaptic Pten loss provides an advantage to dendritic spines in competition over a limited pool of presynaptic boutons. Retrograde monosynaptic tracing with rabies virus reveals that this results in synaptic contact with more presynaptic partners. Using independently excitable opsins to interrogate multiple inputs onto a single neuron, we found that excess connectivity is established indiscriminately from among glutamatergic afferents. Therefore, Pten loss results in inappropriate connectivity whereby neurons are coupled to a greater number of synaptic partners.

Neogenin Promotes BMP2 Activation of YAP and Smad1 and Enhances Astrocytic Differentiation in Developing Mouse Neocortex.

UNLABELLED: Neogenin, a DCC (deleted in colorectal cancer) family receptor, is highly expressed in neural stem cells (NSCs). However, its function in NSCs remains to be explored. Here we provide in vitro and in vivo evidence for neogenin's function in NSCs to promote neocortical astrogliogenesis, but not self-renewal or neural differentiation. Mechanistically, neogenin in neocortical NSCs was required for BMP2 activation of YAP (yes associated protein). The active/nuclear YAP stabilized phospho-Smad1/5/8 and was necessary for BMP2 induction of astrocytic differentiation. Deletion of yap in mouse neocortical NSCs caused a similar deficit in neocortical astrogliogenesis as that in neogenin mutant mice. Expression of YAP in neogenin mutant NSCs diminished the astrocytic differentiation deficit in response to BMP2. Together, these results reveal an unrecognized function of neogenin in increasing neocortical astrogliogenesis, and identify a pathway of BMP2-neogenin-YAP-Smad1 for astrocytic differentiation in developing mouse neocortex. SIGNIFICANCE STATEMENT: Astrocytes, a major type of glial cells in the brain, play important roles in modulating synaptic transmission and information processing, and maintaining CNS homeostasis. The abnormal astrocytic differentiation during development contributes to dysfunctions of synaptic plasticity and neuropsychological disorders. Here we provide evidence for neogenin's function in regulation of the neocortical astrocyte differentiation during mouse brain development. We also provide evidence for the necessity of neogenin in BMP2/Smad1-induced astrocyte differentiation through YAP. Thus, our findings identify an unrecognized function of neogenin in mouse neocortical astrocyte differentiation, and suggest a signaling pathway, BMP2-neogenin-YAP-Smad1, underlying astrogliogenesis in developing mouse neocortex.

NDP52 associates with phosphorylated tau in brains of an Alzheimer disease mouse model.

We previously showed that NDP52 (also known as calcoco2) plays a role as an autophagic receptor for phosphorylated tau facilitating its clearance via autophagy. Here, we examined the expression and association of NDP52 with autophagy-regulated gene (ATG) proteins including LC3, as well as phosphorylated tau and amyloid-beta (Aß) in brains of an AD mouse model. NDP52 was expressed not only in neurons, but also in microglia and astrocytes. NDP52 co-localized with ATGs and phosphorylated tau as expected since it functions as an autophagy receptor for phosphorylated tau in brain. Compared to wild-type mice, the number of autophagic vesicles (AVs) containing NDP52 in both cortex and hippocampal regions was significantly greater in AD model mice. Moreover, the protein levels of NDP52 and phosphorylated tau together with LC3-II were also significantly increased in AD model mice, reflecting autophagy impairment in the AD mouse model. By contrast, a significant change in p62/SQSTM1 level was not observed in this AD mouse model. NDP52 was also associated with intracellular Aß, but not with the extracellular Aß of amyloid plaques. We conclude that NDP52 is a key autophagy receptor for phosphorylated tau in brain. Further our data provide clear evidence for autophagy impairment in brains of AD mouse model, and thus strategies that result in enhancement of autophagic flux in AD are likely to be beneficial.

ATP6AP2, a regulator of LRP6/ß-catenin protein trafficking, promotes Wnt/ß-catenin signaling and bone formation in a cell type dependent manner.

Wnt/ß-catenin signaling is critical for various cellular processes in multiple cell types, including osteoblast (OB) differentiation and function. Exactly how Wnt/ß-catenin signaling is regulated in OBs remain elusive. ATP6AP2, an accessory subunit of V-ATPase, plays important roles in multiple cell types/organs and multiple signaling pathways. However, little is known whether and how ATP6AP2 in OBs regulates Wnt/ß-catenin signaling and bone formation. Here we provide evidence for ATP6AP2 in the OB-lineage cells to promote OB-mediated bone formation and bone homeostasis selectively in the trabecular bone regions. Conditionally knocking out (CKO) ATP6AP2 in the OB-lineage cells (Atp6ap2Ocn-Cre) reduced trabecular, but not cortical, bone formation and bone mass. Proteomic and cellular biochemical studies revealed that LRP6 and N-cadherin were reduced in ATP6AP2-KO BMSCs and OBs, but not osteocytes. Additional in vitro and in vivo studies revealed impaired ß-catenin signaling in ATP6AP2-KO BMSCs and OBs, but not osteocytes, under both basal and Wnt stimulated conditions, although LRP5 was decreased in ATP6AP2-KO osteocytes, but not BMSCs. Further cell biological studies uncovered that osteoblastic ATP6AP2 is not required for Wnt3a suppression of ß-catenin phosphorylation, but necessary for LRP6/ß-catenin and N-cadherin/ß-catenin protein complex distribution at the cell membrane, thus preventing their degradation. Expression of active ß-catenin diminished the OB differentiation deficit in ATP6AP2-KO BMSCs. Taken together, these results support the view for ATP6AP2 as a critical regulator of both LRP6 and N-cadherin protein trafficking and stability, and thus regulating ß-catenin levels, demonstrating an un-recognized function of osteoblastic ATP6AP2 in promoting Wnt/LRP6/ß-catenin signaling and trabecular bone formation.

Optically active conjugated polymer from solvent chirality transfer polymerization in monoterpenes.

Disubstituted acetylene monomers [1,2-diphenylacetylenes (DPAs: DPA-pC1, DPA-mC1, DPA-pC8); 1-phenyl-2-hexylacetylene (PHA-pC1)] are tested for asymmetric polymerization in chiral monoterpenes used as solvents and compared with the corresponding monosubstituted acetylene monomer [1-phenylacetylene (PA-pC1)]. DPA-pC1 containing a trimethylsilyl group in the para-position of the phenyl ring produces an optically active polymer with a large Cotton effect, despite the absence of a stereogenic center. The polymer sample obtained by polymerization in 87% ee (-)-α-pinene shows the strongest CD signal (gCD value at 385 nm: ∼3.2 × 10⁻³). The Cotton bands of the polymers obtained in (-)- and (+)-α-pinenes show the opposite sign in the CD signals. Theoretical calculations show that only the cis-cisoid model adopts a helical conformation. A time-correlated single photon counting experiment shows that the emission of the chiral polymer originates from a virtually single excited species with a 98% component fraction. This polymer solution does not show any significant decrease in gCD value over a wide temperature range of 20 to 80 °C. No noticeable decrease in the gCD value is detected when the polymer solution is kept at relatively low temperatures for a prolonged period (35 d). In contrast, the other polymers show no CD signal.

Multi-omic approach characterises the neuroprotective role of retromer in regulating lysosomal health.

Retromer controls cellular homeostasis through regulating integral membrane protein sorting and transport and by controlling maturation of the endo-lysosomal network. Retromer dysfunction, which is linked to neurodegenerative disorders including Parkinson's and Alzheimer's diseases, manifests in complex cellular phenotypes, though the precise nature of this dysfunction, and its relation to neurodegeneration, remain unclear. Here, we perform an integrated multi-omics approach to provide precise insight into the impact of Retromer dysfunction on endo-lysosomal health and homeostasis within a human neuroglioma cell model. We quantify widespread changes to the lysosomal proteome, indicative of broad lysosomal dysfunction and inefficient autophagic lysosome reformation, coupled with a reconfigured cell surface proteome and secretome reflective of increased lysosomal exocytosis. Through this global proteomic approach and parallel transcriptomic analysis, we provide a holistic view of Retromer function in regulating lysosomal homeostasis and emphasise its role in neuroprotection.

Neogenin inhibits HJV secretion and regulates BMP-induced hepcidin expression and iron homeostasis.

Neogenin, a deleted in colorectal cancer (DCC) family member, has been identified as a receptor for the neuronal axon guidance cues netrins and repulsive guidance molecules repulsive guidance molecules (RGM). RGMc, also called hemojuvelin (HJV), is essential for iron homeostasis. Here we provide evidence that neogenin plays a critical role in iron homeostasis by regulation of HJV secretion and bone morphogenetic protein (BMP) signaling. Livers of neogenin mutant mice exhibit iron overload, low levels of hepcidin, and reduced BMP signaling. Mutant hepatocytes in vitro show impaired BMP2 induction of Smad1/5/8 phosphorylation and hepcidin expression. Neogenin is expressed in liver cells in a reciprocal pattern to that of hepcidin, suggesting that neogenin functions in a cell nonautonomous manner. Further studies demonstrate that neogenin may stabilize HJV, a glycosylphosphatidylinositol-anchored protein that interacts with neogenin and suppresses its secretion. Taken together, our results lead the hypothesis that neogenin regulates iron homeostasis via inhibiting secretion of HJV, an inhibitor of BMP signaling, to enhance BMP signaling and hepcidin expression. These results reveal a novel mechanism underlying neogenin regulation of HJV-BMP signaling.

Retrograde regulation of motoneuron differentiation by muscle beta-catenin.

Synapse formation requires proper interaction between pre- and postsynaptic cells. In anterograde signaling, neurons release factors to guide postsynaptic differentiation. However, less is known about how postsynaptic targets retrogradely regulate presynaptic differentiation or function. We found that muscle-specific conditional knockout of beta-catenin (Ctnnb1, also known as beta-cat) in mice caused both morphologic and functional defects in motoneuron terminals of neuromuscular junctions (NMJs). In the absence of muscle beta-catenin, acetylcholine receptor clusters were increased in size and distributed throughout a wider region. Primary nerve branches were mislocated, whereas secondary or intramuscular nerve branches were elongated and reduced in number. Both spontaneous and evoked neurotransmitter release was reduced at the mutant NMJs. Furthermore, short-term plasticity and calcium sensitivity of neurotransmitter release were compromised in beta-catenin-deficient muscle. In contrast, the NMJ was normal in morphology and function in motoneuron-specific beta-catenin-deficient mice. Taken together, these observations indicate a role for muscle beta-catenin in presynaptic differentiation and function, identifying a previously unknown retrograde signaling in the synapse formation and synaptic plasticity.

Critical Role of Neuronal Vps35 in Blood Vessel Branching and Maturation in Developing Mouse Brain.

Vps35 (vacuolar protein sorting 35), a key component of retromer, plays a crucial role in selective retrieval of transmembrane proteins from endosomes to trans-Golgi networks. Dysfunctional Vps35/retromer is a risk factor for the development of neurodegenerative diseases. Vps35 is highly expressed in developing pyramidal neurons, both in the mouse neocortex and hippocampus, Although embryonic neuronal Vps35's function in promoting neuronal terminal differentiation and survival is evident, it remains unclear whether and how neuronal Vps35 communicates with other types of brain cells, such as blood vessels (BVs), which are essential for supplying nutrients to neurons. Dysfunctional BVs contribute to the pathogenesis of various neurodegenerative disorders. Here, we provide evidence for embryonic neuronal Vps35 as critical for BV branching and maturation in the developing mouse brain. Selectively knocking out (KO) Vps35 in mouse embryonic, not postnatal, neurons results in reductions in BV branching and density, arteriole diameter, and BV-associated pericytes and microglia but an increase in BV-associated reactive astrocytes. Deletion of microglia by PLX3397 enhances these BV deficits in mutant mice. These results reveal the function of neuronal Vps35 in neurovascular coupling in the developing mouse brain and implicate BV-associated microglia as underlying this event.

Radiographic changes of mandibular cortical bone in bisphosphonate drug holiday.

Objectives: There have been few studies to date on the residual effect of bisphosphonate. This study investigated the radiographic changes of mandibular cortical thickness upon bisphosphonate drug holiday. Materials and Methods: This retrospective study includes 36 patients diagnosed with MRONJ (medication-related osteonecrosis of the jaw) at Ajou University Dental Hospital in 2010-2021. All patients stopped taking bisphosphonate under consultation with the prescribing physicians. Panoramic radiographs were taken at the start of discontinuation (T0), 12 months after (T1), and 18 months after (T2) discontinuation of bisphosphonate, respectively. Mental index and panoramic mandibular index were calculated using Ledgerton's method. Paired t-tests were used to analyze differences over time. Results: The difference in indices (mental index and panoramic mandibular index) between T0 and T1 was not statistically significant (paired t-test, P>0.05). However, the difference in these indices between T1 and T2 was statistically significant (paired t-test, P<0.05). Conclusion: The cortical thickness of the mandible decreased in the late stage (after 18 months) as observed by panoramic radiograph.

Muscular Swedish mutant APP-to-Brain axis in the development of Alzheimer's disease.

Alzheimer's disease (AD) is the most common form of dementia. Notably, patients with AD often suffer from severe sarcopenia. However, their direct link and relationship remain poorly understood. Here, we generated a mouse line, TgAPPsweHSA, by crossing LSL (LoxP-STOP-LoxP)-APPswe with HSA-Cre mice, which express APPswe (Swedish mutant APP) selectively in skeletal muscles. Examining phenotypes in TgAPPsweHSA mice showed not only sarcopenia-like deficit, but also AD-relevant hippocampal inflammation, impairments in adult hippocampal neurogenesis and blood brain barrier (BBB), and depression-like behaviors. Further studies suggest that APPswe expression in skeletal muscles induces senescence and expressions of senescence-associated secretory phenotypes (SASPs), which include inflammatory cytokines and chemokines; but decreases growth factors, such as PDGF-BB and BDNF. These changes likely contribute to the systemic and hippocampal inflammation, deficits in neurogenesis and BBB, and depression-like behaviors, revealing a link of sarcopenia with AD, and uncovering an axis of muscular APPswe to brain in AD development.

Hepcidin contributes to Swedish mutant APP-induced osteoclastogenesis and trabecular bone loss.

Patients with Alzheimer's disease (AD) often have lower bone mass than healthy individuals. However, the mechanisms underlying this change remain elusive. Previously, we found that Tg2576 mice, an AD animal model that ubiquitously expresses Swedish mutant amyloid precursor protein (APPswe), shows osteoporotic changes, reduced bone formation, and increased bone resorption. To understand how bone deficits develop in Tg2576 mice, we used a multiplex antibody array to screen for serum proteins that are altered in Tg2576 mice and identified hepcidin, a master regulator of iron homeostasis. We further investigated hepcidin's function in bone homeostasis and found that hepcidin levels were increased not only in the serum but also in the liver, muscle, and osteoblast (OB) lineage cells in Tg2576 mice at both the mRNA and protein levels. We then generated mice selectively expressing hepcidin in hepatocytes or OB lineage cells, which showed trabecular bone loss and increased osteoclast (OC)-mediated bone resorption. Further cell studies suggested that hepcidin increased OC precursor proliferation and differentiation by downregulating ferroportin (FPN) expression and increasing intracellular iron levels. In OB lineage cells, APPswe enhanced hepcidin expression by inducing ER stress and increasing OC formation, in part through hepcidin. Together, these results suggest that increased hepcidin expression in hepatocytes and OB lineage cells in Tg2576 mice contributes to enhanced osteoclastogenesis and trabecular bone loss, identifying the hepcidin-FPN-iron axis as a potential therapeutic target to prevent AD-associated bone loss.

Osteoblastic Swedish mutant APP expedites brain deficits by inducing endoplasmic reticulum stress-driven senescence.

Patients with Alzheimer's disease (AD) often have osteoporosis or osteopenia. However, their direct link and relationship remain largely unclear. Previous studies have detected osteoporotic deficits in young adult Tg2576 and TgAPPsweOCN mice, which express APPswe (Swedish mutant) ubiquitously and selectively in osteoblast (OB)-lineage cells. This raises the question, whether osteoblastic APPswe contributes to AD development. Here, we provide evidence that TgAPPsweOCN mice also exhibit AD-relevant brain pathologies and behavior phenotypes. Some brain pathologies include age-dependent and regional-selective increases in glial activation and pro-inflammatory cytokines, which are accompanied by behavioral phenotypes such as anxiety, depression, and altered learning and memory. Further cellular studies suggest that APPswe, but not APPwt or APPlon (London mutant), in OB-lineage cells induces endoplasmic reticulum-stress driven senescence, driving systemic and cortex inflammation as well as behavioral changes in 6-month-old TgAPPsweOCN mice. These results therefore reveal an unrecognized function of osteoblastic APPswe to brain axis in AD development.